Measuring Fuels

How are fuels measured in chaparral?

The fire spread predictions used in the current United States fire prediction system are based upon a semi-empirical formulation first presented by Rothermel in 1972. This system has been implemented operationally in the form of programmable hand-held calculators in the late 1970s (Rothermel, 1983), the BEHAVE minicomputer program in the middle 1980s (Andrews, 1986), and the FARSITE fire spread model in the middle 1990s (Finney, 1998). The Rothermel fire behavior model, and variants thereof, require detailed stand-level vegetation properties listed in table below in order to accurately predict fire spread.

Vegetation Related Fuel Properties For Chaparral
Property Name	Measurement	Units	Spatial Variability
Dead 1 Hour Fuels	Stem Diameter < 0.635 cm	Mg/ha	varies spatially
Dead 1 Hour Surface-Area-To-Volume	Estimated	cm2/cm3	constant with species
Dead 1 Hour Fuel Moisture	(Wet-Dry Weight) / Dry Weight	%	varies spatially & temporally (diurnal)
Dead 10 Hour Fuels	Stem Diameter 0.635 - 2.54 cm	Mg/ha	varies spatially
Dead 10 Hour Surface-Area-To-Volume	Estimated	cm2/cm3	constant with species
Dead 10 Hour Fuel Moisture	(Wet-Dry Weight) / Dry Weight	%	varies spatially & temporally (diurnal)
Dead 100 Hour Fuels	Stem Diameter 2.54 - 7.62 cm	Mg/ha	varies spatially
Dead 100 Hour Surface-Area-To-Volume	Estimated	cm2/cm3	constant with species
Dead 100 Hour Fuel Moisture	(Wet-Dry Weight) / Dry Weight	%	varies spatially & temporally (diurnal)
Live Herbaceous Fuels	All, regardless of diameter	Mg/ha	varies spatially
Live Herbaceous Surface-Area-To-Volume	Estimated	cm2/cm3	constant with species
Live Woody Fuels	Stem Diameter < 0.635 cm	Mg/ha	varies spatially
Live Woody Surface-Area-To-Volume	Estimated	cm2/cm3	constant with species
Live Fuel Moisture	(Wet-Dry Weight) / Dry Weight	%	varies spatially & temporally (seasonal)
Fuel Bed Depth	Estimated	m	varies spatially
Heat Content of Dead Fuels	Estimated	kJ/kg	constant with species
Heat Content of Live Fuels	Estimated	kJ/kg	constant with species
Moisture of Extinction of Dead Fuels	(Wet-Dry Weight) / Dry Weight	%	constant with species
		Note: The fuel "hour" class corresponds to the fuel diameter and is a direct reference to the amount of time it takes for an idealized cylinder of vegetation of that size to reach equilibrium moisture content (EMC).